Systems and methods for blind equalization in a digital receiver
View Patent ↗A digital receiver system to recover signals from inter-symbol-interference includes a finite impulse response (FIR) filter using convolution to recover signals; and a channel estimator coupled to the FIR filter to estimate FIR coefficients, wherein the channel estimator uses a second order expectation and a fourth order expectation from a convolution to calculate error function.
1. A digital receiver system to recover signals from inter-symbol-interference, comprising:
a. a finite impulse response (FIR) filter using convolution to recover signals; and
b. a channel estimator coupled to the FIR filter to estimate FIR coefficients, wherein the channel estimator uses a second order expectation and a fourth order expectation from a convolution to calculate error function, the second and fourth order expectations are determined in parallel, and multiple expectation results are added together for accuracy.
2. The receiver of claim 1 , wherein the channel estimator determines the second and fourth order expectations x i 2 * and x i 4 * of a channel output signal by averaging the channel output signal
E└x i 1 (k)x i 2 *(k−l 1 )x i 3 *(k−l 2 )x i 4 *(K−l 3 )┘ and E└x i 1 (k)x i 2 *(k−l 1 )┘,
for l 1 , l 2 , l 3 ε{−L w , . . . , L w } and i 1 , i 2 , i 3 , i 4 ε{1, . . . , p}.
3. The receiver of claim 1 , wherein the channel estimator uses a steepest descent or ascent process to achieve convergence and wherein gradients are determined for each update.
4. The receiver of claim 1 , wherein the second and fourth order expectations are determined based on a batch of input.
5. The receiver of claim 4 , wherein the expectations from the batch are provided to an equalizer error function to update coefficients.
6. The receiver of claim 1 , wherein multiple expectation results are added together and update an error function.
7. The receiver of claim 1 , wherein the second and fourth order expectations are determined separately from an equalization error determination.
8. The receiver of claim 1 , wherein the channel estimator comprises a blind equalizer.
9. The receiver of claim 8 , wherein the channel estimator comprises a Constant Modulus Algorithm (CMA) equalizer.
10. The receiver of claim 9 , wherein the CMA equalizer comprises an error function with steepest descent or ascent.
11. The receiver of claim 1 , wherein only inputs are used to update coefficients in an open loop and outputs are not used for coefficient updating.
12. The receiver of claim 1 , where the convolution is done in frequency domain using multiplication.
13. A digital receiver system to recover signals from inter-symbol-interference, comprising:
a. a finite impulse response (FIR) filter using convolution to recover signals; and
b. a channel estimator coupled to the FIR filter to estimate FIR coefficients, wherein the channel estimator uses a second order expectation and a fourth order expectation from a convolution to calculate error function, the second and fourth order expectations are determined in parallel and multiple expectation results are added together and an error function is updated.
14. A digital receiver system to recover signals from inter-symbol-interference, comprising:
c. a finite impulse response (FIR) filter using convolution to recover signals; and
d. a channel estimator coupled to the FIR filter to estimate FIR coefficients, wherein the channel estimator uses a second order expectation and a fourth order expectation from a convolution to calculate error function and the second and fourth order expectations are determined separately from an equalization error determination.